RESUMO
Nigroxins A and B, two myotoxic phospholipases A2 (PLA2s) from the venom of the American elapid Micrurus nigrocinctus, belong to a new PLA2 subclass. Their primary structures were established and compared with those of PLA2s that have already been studied with respect to myotoxic activity. The combination of amino acid residues Arg15, Ala100, Asn108 and a hydrophobic residue at position 109 is present exclusively in class I PLA2s that display myotoxic activity. These residues cluster within a surface region rich in positive charges and are suggested to play a role in the interaction with the target membrane of the muscle fibers. It is concluded that the myotoxic PLA2s resulted from recruitment of an ancient scaffold. Dendrotoxins and alpha-neurotoxins are similarly derived from other old structures, which are, however, now also present in nontoxic proteins that are widely distributed throughout the animal kingdom. The evolutionary pathways by which elapid PLA2s acquired myotoxicity and dendrotoxins acquired K+-channel blocker activity are traced. They demonstrate how existing scaffolds were adapted stepwise to serve toxic functions by exchange of a few surface-exposed residues.
Assuntos
Venenos Elapídicos/química , Elapidae , Evolução Molecular , Peptídeos/química , Fosfolipases A/química , Sequência de Aminoácidos , Animais , Análise por Conglomerados , Sequência Conservada , Reações Cruzadas , Venenos Elapídicos/classificação , Venenos Elapídicos/imunologia , Fosfolipases A2 do Grupo I , Camundongos , Modelos Moleculares , Dados de Sequência Molecular , Músculo Esquelético/efeitos dos fármacos , Peptídeos/classificação , Peptídeos/imunologia , Fosfolipases A/classificação , Fosfolipases A/imunologia , Fosfolipases A2 , Inibidores de Proteases/química , Proteínas de Répteis , Homologia de Sequência de Aminoácidos , Relação Estrutura-Atividade , Toxinas Biológicas/química , Toxinas Biológicas/classificação , Toxinas Biológicas/imunologiaRESUMO
The presence of multiple nicotinic acetylcholine receptor (AchR)-binding proteins and phospholipases A2 was detected in the venom of a member of the Elapinae subfamily, Micrurus nigrocinctus nigrocinctus. Multi-step chromatographies were used to isolate four AchR-binding proteins (Mnn-9, Mnn-4, Mnn-3C and Mnn-1A) and five basic PLA2s (nigroxins A, B, C1, C2 and C3). The Micrurus AchR-binding proteins are antigenically and structurally related to short- and long-chain alpha-neurotoxins from Naja. The nigroxins are antigenically similar and constitute a new antigenic subclass of PLA(2)s. Nigroxins A and B are class I PLA(2)s, structurally more related to enzymes from Bungarinae than to those from Hydrophinae/Laticaudinae. These data contribute to clarify the relationships between Micrurus venom proteins and other elapid toxins and may be useful to improve the neutralizing efficiency of antivenoms.